Adding class for generating all subsequences from a given List (#5194)

* Adding class for generating all subsequences from a given List

* Fix test data format

* Fix braces wrong placement

* Fix "Utility classes should not have a public or default constructor."

* Fix checkstyle " Class Subsequence should be declared as final."

* Renaming class Subsequence to SubsequenceFinder. Refactored test to Parametrized test. Fixed input parameter as final.

* Fix formatting

* Fix formatting

* Fix formatting

* Fix import ordering

* Renaming method generate all.
Renaming test method.
Adding duplication test.
Renaming TestData to TestCase.

* Fix formatting

* style: add assertion to avoid potential infinite loop

---------

Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

src/test/java/com/thealgorithms/backtracking/SubsequenceFinderTest.java

@@ -0,0 +1,28 @@
+package com.thealgorithms.backtracking;
+
+import static org.junit.jupiter.api.Assertions.assertIterableEquals;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Stream;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.MethodSource;
+
+public class SubsequenceFinderTest {
+
+    @ParameterizedTest
+    @MethodSource("getTestCases")
+    void testGenerateAll(TestCase testData) {
+        final var actual = SubsequenceFinder.generateAll(testData.input());
+        assertIterableEquals(testData.expected(), actual);
+    }
+
+    static Stream<TestCase> getTestCases() {
+        return Stream.of(new TestCase(new ArrayList<>(), List.of(List.of())), new TestCase(List.of(1, 2), List.of(List.of(), List.of(2), List.of(1), List.of(1, 2))),
+            new TestCase(List.of("A", "B", "C"), List.of(List.of(), List.of("C"), List.of("B"), List.of("B", "C"), List.of("A"), List.of("A", "C"), List.of("A", "B"), List.of("A", "B", "C"))),
+            new TestCase(List.of(1, 2, 3), List.of(List.of(), List.of(3), List.of(2), List.of(2, 3), List.of(1), List.of(1, 3), List.of(1, 2), List.of(1, 2, 3))), new TestCase(List.of(2, 2), List.of(List.of(), List.of(2), List.of(2), List.of(2, 2))));
+    }
+
+    record TestCase(List<Object> input, List<List<Object>> expected) {
+    }
+}